The general rule is that you are stuck with the record on appeal and can’t supplement it with new or additional facts.
There are however some limited exceptions to the general rule for items of appellate judicial notice. Here is a short piece discussing some of the exceptions.
An example from military appeals:
The ACCA is permitted to take appellate judicial notice of other dispositions in similar cases, and the defense needs information to start and focus that judicial notice. See United States v. Smith, 56 M.J. 653, 659 n.7 (Army Ct. Crim. App. 2001)(collecting cases establishing an appellate court’s authority to judicially notice other records or portions thereof in exercising its Article 66, UCMJ authority).